Mark internal _itoa functions hidden

Since internal _itoa functions are only used internally in ld.so and
libc.so, they can be made hidden.

	[BZ #19122]
	* sysdeps/generic/_itoa.h (_itoa): Add attribute_hidden.
	(_itoa_word): Likewise.

ChangeLog

@@ -1,6 +1,9 @@
 2015-10-15  H.J. Lu  <hongjiu.lu@intel.com>
 
 	[BZ #19122]
+	* sysdeps/generic/_itoa.h (_itoa): Add attribute_hidden.
+	(_itoa_word): Likewise.
+
 	* elf/dl-runtime.c (_dl_fixup): Add attribute_hidden.
 	* elf/dynamic-link.h (_dl_try_allocate_static_tls): Likewise.
 	* sysdeps/generic/dl-cache.h (_dl_cache_libcmp): Likewise.

sysdeps/generic/_itoa.h

@@ -42,7 +42,7 @@
    Use upper case letters iff UPPER_CASE is nonzero.  */
 
 extern char *_itoa (unsigned long long int value, char *buflim,
-		    unsigned int base, int upper_case);
+		    unsigned int base, int upper_case) attribute_hidden;
 
 extern const char _itoa_upper_digits[];
 extern const char _itoa_lower_digits[];
@@ -53,7 +53,8 @@ hidden_proto (_itoa_lower_digits)
 
 #if IS_IN (libc)
 extern char *_itoa_word (_ITOA_WORD_TYPE value, char *buflim,
-			 unsigned int base, int upper_case);
+			 unsigned int base,
+			 int upper_case) attribute_hidden;
 #else
 static inline char * __attribute__ ((unused, always_inline))
 _itoa_word (_ITOA_WORD_TYPE value, char *buflim,